In a vehicle seat assembly hinge it is common to have one hinge plate, which is typically connected to a seat back member, sandwiched between and connected in hinged relation to a pair of generally opposed hinged plates, which are typically connected to a seat cushion member. Other similar arrangements may also be used. It is well known to connect the single hinge plate to the pair of hinge plates in hinged relation by a pivot pin that is received in close-fitting operative engagement in aligned openings in all of the hinge members. The pivot pin is typically connected in rigid and generally unmoving relation to the pair of hinge plates and the remaining sandwiched hinge plate rotates about an annular hub portion of the pivot pin. It is also possible to have the pivot pin rigidly connected to the sandwiched hinge plate and rotate with respect to the pair of hinge plates.
It is important that the pivot pin be rotationally and axially fixed with respect to the hinge plate or plates it is connected to, such that there is little or no rotational movement and also little or no axially directed movement of the pivot pin with respect to the plate or plates. Further, it is important that the pivot pin remains rotationally fixed and axially fixed as described above for an extended period of time, preferably in the order of 75,000 cycles of operation of the vehicle seat assembly hinge. It is well known that if the pivot pin becomes loose, there will be a general looseness in the vehicle seat assembly hinge, which in turn could cause an increased and generally unacceptable amount of chuck in the seat back member, or could even cause a malfunction of the hinge.
There are several well known methods of connecting the pivot pin in rigid and unmoving relation to the pair of hinge plates connected to the seat cushion member, which will be discussed henceforth.
One method of connecting the pivot pin in generally rigid and unmoving relation to the pair of hinge plates as aforesaid involves providing a pair of flats on the pivot pin and having corresponding flat surfaces on an opening in an at least one of the pair of hinge plates, which pair of flats and corresponding flat surfaces preclude the pivot pin from rotational movement with respect to the outer hinge plates. This method is fully described and detailed in U.S. Pat. No. 4,875,735 to Moyer et al., which patent is incorporated herein by reference. Machining of the flats is, however, a costly process step, and normal manufacturing tolerances result in clearances between the flats and the corresponding flat surfaces on the opening(s) of the hinge plate(s), such that some undesired rotation of the pivot pin is typically encountered.
Another method is known as "C" clipping. A portion of the pivot pin exterior to the outermost hinge plates has a circumferential groove machined therein at one or both ends thereof. After the pivot pin is inserted into the openings in the hinge plates, the "C" clip is inserted into the circumferential groove or grooves, thereby retaining and precluding axially directed movement of the pivot pin. However, the pivot pin is not necessarily held tightly against the outer surfaces of the respective two outer hinge plates, such that the "C" clip does not preclude rotational movement of the pivot pin. Moreover, use of a "C" clip to retain a pivot pin in this general manner is costly because it involves one or two extra parts, (i.e., the "C" clips) an extra manufacturing step to machine the circumferential rings on the pivot pin, and also an extra assembly step to attach the "C" clip or clips. An example of "C" clipping can be seen in U.S. Pat. No. 4,707,010 issued to Croft and Hiscox, which patent is incorporated herein by reference.
Another method of connecting the pivot pin in generally rigid and unmoving relation to the outer plates is known as orbital staking, which is essentially simple riveting. In orbital staking, the ends of the pivot pin extend a small amount beyond the outer surfaces of the outermost hinge plates. These ends of the pivot pin are compressed by a hydraulic press such that they flare outwardly and over the outer surface of the respective hinge plate until the flared portion comes into intimate and tight contact with that outer surface. The friction between each flared portion and the outer surfaces of the hinge plates precludes the pivot pin from moving rotationally. The flared portions preclude the pivot pin from axial movement. The pin generally remains tightly engaged with the hinge plates in the short term. However, it has been found that pins secured by orbital staking do not stand up in long term service, as they tend to loosen, whereafter they can no longer resist rotational movement.
A further method, which is similar to orbital staking, is known as ring staking. Ring staking involves the plastic deformation of the ends of plastically deformable pivot pin material into the very narrow annular gap between the pivot pin and the surface of the opening in the hinge plates. This deformed pivot pin material is pressed under great force into the annular gap, thus causing extremely high friction between the deformed material and the hinge plates, and between the deformed material and the pivot pin. Pivot pins secured by ring staking are generally unmovable within the hinge plates with respect to rotational movement and also with respect to axial movement, over the short term. Ring staking produces somewhat better results than orbital staking with respect to precluding rotational movement over the long term, but still does not stand up in long term service as well as is required in the automotive industry. It has been found that after about 25,000 cycles of use, a pivot pin secured in this manner becomes worn and loose, and is apt to allow rotational movement of the pivot pin. It has further been shown that shearing of the pivot pin may readily occur at about 50,000 to about 55,000 cycles of use.
It is therefore desirable to produce a method of securing a pivot pin in a hinge plate such that rotational movement of the pin with respect to the hinge plate is precluded over the long term for at least 75,000 cycles.
It is an object of the present invention to produce a pivot pin and an improved vehicle seat assembly hinge containing such a pivot pin, that substantially precludes axially directed movement and rotational movement.
It is another object of the invention to produce a vehicle seat assembly hinge having a pivot pin that remains axially tight and rotationally unmovable therein for about 75,000 cycles or more.
It is a further object of the invention to produce a pivot pin and a vehicle seat assembly hinge that are relatively inexpensive to manufacture and easy to assemble.
Other objects, features and characteristics of the present invention, as well as methods of operation and functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification.